1. Field of the Invention
The present invention relates generally to the field of gunshot and explosion detection, and more particularly, to a system and device for detecting the nearfield presence of gunfire and/or explosions by evaluating the acoustic energy and the instantaneous change of localized air pressure when a gun is discharged or an explosive device detonated.
2. Description of the Related Art
There are a number of inventions that use various typos of sensors to detect projectiles, but none of these inventions combines a microphone with a differential pressure sensor and software that enables gunshots to be differentiated from explosions and single gunshots from multiple gunshots, while at the same time minimizing false positives by differentiating explosive events from non-explosive events.
U.S. Pat. No. 5,241,518 (McNelis et al., 1993) discloses an apparatus and method for determining the trajectory of a supersonic projectile of unknown velocity and direction. The apparatus has at least throe spaced-apart sensors capable of registering a shock wave generated by a supersonic projectile passing in the vicinity of the sensors. The sensors generate signals based on the azimuth and elevation angle of a unit sighting vector from each sensor to the point of origin of the shock wave. A computer then calculates the azimuth and elevation angle of the local trajectory of the projectile.
U.S. Pat. No. 5,544,129 (McNelis, 1996) provides a method and apparatus for determining the general direction of the origin of a projectile. A sensor with three spaced-apart transducers generates signals in response to a blast wave created at an origin of a projectile. The signals generated by the transducers enable a time relation to be measured among the three transducers as the blast wave serially encounters each of the three transducers. From the time relations, a sighting vector from the sensor to the origin of the blast wave is determined.
U.S. Pat. No. 5,930,202 (Duckworth et al., 1999) and U.S. Pat. No. 6,178,141 (Duckworth et al., 2001) describe a sniper detection and localization system that uses observations of the shock wave from supersonic bullets to estimate the bullet trajectory, Mach number and caliber. The system uses a distributed array of acoustic sensors to detect the leading edge of a projectile's shock wave and the muzzle blast from a firearm. This information is then used to measure the wave arrival times of each waveform type at the sensors. This time of arrival information determines the projectile's trajectory and a line of bearing to the origin of the projectile.
U.S. Pat. No. 6,281,792 (Lerg et al., 2001) involves a system and method for detecting a firearm shot. The system uses one or more sonic sensors that sense the firearm shot and transmit a signal to a base unit that processes the signal and determines whether it represents a firearm shot. A communication device communicates to one or more entities that a firearm shot has been detected and provides an alarm indicating that the firearm shot took place.
U.S. Pat. No. 7,126,877 (Barger et al., 2006) and U.S. Pat. No. 7,408,840 (Barger et al., 2008) disclose a system and method for locating shooters of supersonic projectiles based on shockwave measurements only. The system incorporates five to seven sensors set at least one meter apart. The sensor signals are processed by computer software to generate a shockwave arrival angle unit vector. Two different methods are described; one method uses counters in each signal channel and another method uses cross-correlation between signal channels.
U.S. Pat. No. 7,266,045 (Baxter et al., 2007), U.S. Pat. No. 7,688,679 (Baxter et al., 2010) and U.S. Pat. No. 8,036,065 (Baxter et al., 2011) provide a system and method for locating and identifying an acoustic event such as gunfire. The system incorporates a plurality of person-wearable acoustic sensors, each having a display for displaying information to the user. The sensor includes a microphone, an A/D converter, a processor, a GPS receiver, and a network interface. The processor processes a digitized signal to detect a gunshot and determine a time of arrival.
U.S. Pat. No. 7,750,814 (Fisher et al., 2010) describes an acoustic sensor that can be worn by a person for detecting gunshot events. The sensor has a housing, a microphone, a processor, a GPS receiver, and a display. The sensor is either integrated into a piece of equipment normally carried by a soldier, integrated into an article of clothing, or secured to such a piece of equipment or article of clothing.
U.S. Pat. No. 8,050,141 (Carroll et al., 2011) involves a system and method for estimating a trajectory of an incoming bullet based on the acoustics of the shock wave created as the bullet travels through the air. A first auditory signal representing a direct sound from the shock wave is recorded and its azimuthal direction determined. A second auditory signal representing a reflection of the shock wave as it travels through the air is also recorded and its azimuthal direction determined. These two signals are used to determine an estimated direction of the bullet source.
U.S. Pat. No. 8,111,582 (Beck et al. 2012) covers user-wearable sensor arrays for use with projectile-detection systems. The sensor array comprises a plurality of sensors configured to detect at least one of sound waves and pressure waves caused by at least one of the muzzle blast and shockwave of a projectile and a collar that supports the sensors.
U.S. Pat. No. 8,325,563 (Calhoun et al., 2012) discloses systems and methods for locating weapon fire incidents using data from acoustic, optical, seismic and/or other sensors. The invention includes a method for locating the incident from a combination of propagation phenomena including a discharge time of the weapon fire incident. The method may include processing the data from various signals to determine the location using a common time basis among sensor measurements.
U.S. Patent Application Pub. No. 2008/0008044 (Patterson et al.) provides a system for detecting acoustic events comprising a wearable sensor with a microprocessor, a microphone communicating with the microprocessor, a GPS module, and a display screen. The microphone allows the microprocessor to detect the acoustic event, the GPS determines the location of the wearable sensor, and the system triangulates the location and time of the acoustic event to detect gunshots. A wireless network system allows for the interfacing and sharing of data between the sensor and other components of the system.
U.S. Patent Application Pub. Nos. 2012/0177219 (Mullen et al.), 2012/0182834 (Mullen et al.), and 2012/0275272 (Mullen et al.) describe a wearable shooter localization system that includes a microphone array, processor and output device. The microphone array senses acoustic events caused by gunfire and provides electrical signals to the processing unit. The system optionally includes orientation and/or motion detection sensors that are used to initially compute a direction to the origin of a projectile in a frame of reference that is meaningful to the wearer or to subsequently update that direction as the wearer moves.
U.S. Patent Application Pub. No. 2014/0190051 (Wichner) discusses an apparatus, device or method for detecting am or pointing direction of a firearm. The method involves detecting a sound signature from of a gunshot from the firearm, sensing an aim direction of the firearm at the time of the sound signal, setting a reference direction, sensing a current aim direction and comparing it to the reference direction, and initiating an alarm if the current aim direction is beyond a threshold angle of displacement from the reference direction.
Many of the prior art references discussed above, including, but not limited to, U.S. Pat. No. 7,266,045 (Baxter et al., 2007), U.S. Pat. No. 7,688,679 (Baxter et al., 2010) and U.S. Pat. No. 8,036,065 (Baxter et al., 2011), involve determining the location of the gunshot based on time difference of arrival from multiple audio sensors that are physically separated by relatively large distances. The present invention, on the other hand, is a nearfield gunshot device that utilizes a differential air pressure sensor in addition to an audio sensor (both contained within a single device) to detect gunshots and other explosive events. The system described in the Baxter patents use a call center to validate the gunshot audio signal and decide whom to contact (in other words, the system requires human intervention). Furthermore, the Baxter system requires more than one device to generate the location information (based on time difference of arrival). The present invention does not require a call center, does not depend upon time difference of arrival, and a single device is all that is needed to determine that a gunshot has occurred within proximity of the device location. As used herein, the term “nearfield” means within an enclosed room or within approximately five meters of a person wearing the device outside.